<dt style="font-weight: bold">-R</dt><dd>Do a reverse sync. Normally, messages would be pushed from the local system to the destination(remote). This option reverses the flow, and will instead pull messages from the remote to thelocal storage.</dd>

dsync is Dovecot's mailbox synchronization utility. It can be used for several different use
cases: Two-way synchronization of mailboxes, creating backups of mails, and convert mailboxes
from/to different mailbox formats. All of these can be used within the same server or between
different servers (via ssh(1) or tcp
connections). Remote mailboxes can be accessed also via IMAP protocol, which allows using dsync for
mailbox migration purposes.

You can run dsync in one of three modes:

*

doveadm backup performs one-way synchronization. If there are any changes in the
destination they will be deleted, so the destination will look exactly like the source.

*

doveadm sync performs two-way synchronization. It merges all changes without losing
anything. Both the mailboxes will end up looking identical after the synchronization is
finished.

*

doveadm sync -1 performs one-way synchronization, but it merges the changes in
destination without deleting anything. This doesn't currently work perfectly, so its use should
be limited. Its main purpose is that during mailbox migration you can run doveadm backup
multiple times, then switch mails to be delivered to the new mailbox and run doveadm sync -1
once more to transfer any last new mails from the old mailbox.

There are also three different synchronization algorithms:

*

Full synchronization (-f parameter) scans through all the messages in all the mailboxes. This
guarantees that everything will be synchronized, but it's unnecessarily slow for incremental
synchronization.

*

Fast synchronization (default) first attempts to find mailboxes that have changed, and
synchronize only those. This is done by checking the mailboxes' metadata (NEXTUID and
HIGHESTMODSEQ). Usually this works fine, especially with one-way synchronization, but if both sides
do exactly the same number of changes, the metadata may end up containing the same values even if
the changes were different.

*

Stateful synchronization (-s parameter) is the most efficient way to synchronize mailboxes. It
relies on having the earlier dsync run's state saved somewhere and being passed to the next
dsync run. Based on this state dsync can send only the changes that happened after the previous
dsync run. As long as the state or the mailboxes aren't corrupted this algorithm should work
perfectly. The replicator process uses this internally to perform most of the synchronization.

The syncing is done as perfectly as possible: an IMAP or a POP3 client shouldn't be able to
notice any differences between the two mailboxes. Two-way syncing means that it's safe to do
any kind of modifications in both sides, and dsync will merge the changes without losing any
changes done on either side. This is possible because dsync can access Dovecot's index logs
that keep track of changes. It's of course possible to have conflicts during merging, these are
resolved in a safe way. See the dsync design document for more information.

dsync uses the same configuration files as the rest of Dovecot (via doveconf(1) binary). The entire configuration can be changed by giving -c
parameter to another configuration file, or using -o parameter to override specific settings. When
executing a remote dsync program it works the same way: it uses its own local configuration.

dsync can be run completely standalone. It doesn't require any Dovecot server processes to
be running, except when using -u parameter to do a userdb lookup from auth process.

dsync can sync either one or multiple users using the -u or -A parameters. For continuous
replication you can use the Dovecot replicator process, which automatically runs dsync whenever
messages have changed.

Overrides the configuration setting from /etc/dovecot/dovecot.conf and from the
userdb with the given value. In order to override multiple settings, the -o option
may be specified multiple times.

-v

Enables verbosity, including progress counter.

Command specific options:

-1

Do one-way synchronization instead of two-way synchronization.

-A

If the -A option is present, the command will be performed for all users. Using
this option in combination with system users from userdb { driver = passwd } is not
recommended, because it contains also users with a lower UID than the one configured with the
first_valid_uid setting.

When the SQL userdb module is used make sure that the iterate_query setting in
/etc/dovecot/dovecot-sql.conf.ext matches your database layout. When using the LDAP userdb
module, make sure that the iterate_attrs and iterate_filter settings in
/etc/dovecot/dovecot-ldap.conf.ext match your LDAP schema. Otherwise doveadm(1) will be unable to iterate over all users.

-F file

Execute the command for all the users in the file. This is similar to the
-A option, but instead of getting the list of users from the userdb, they are read from the
given file. The file contains one username per line.

-N

Synchronize all the available namespaces. By default only namespaces that don't have
explicit location setting are synchronized.

-P

Run a doveadm-purge(1) for the destination (remote)
storage after synchronization.

-R

Do a reverse sync. Normally, messages would be pushed from the local system to the destination
(remote). This option reverses the flow, and will instead pull messages from the remote to the
local storage.

-S socket_path

The option's argument is either an absolute path to a local UNIX domain socket, or a
hostname and port (hostname:port), in order to connect a remote host via a TCP
socket.

This allows an administrator to execute doveadm(1) mail
commands through the given socket.

-T secs

Specify the time in seconds, how long doveadm(1) should
wait for stalled I/O operations. The default timeout is 600 seconds.

-U

This is used internally by replicator to have dsync notify it when the synchronization is
finished.

-d

Use the default destination, which is looked up from the mail_replica userdb extra
field.

-g mailbox_guid

Same as -m, but find the mailbox to be synchronized by its GUID instead of by name.

-l secs

Lock the dsync for this user. Wait for maximum secs before giving up. This parameter
should be used to avoid broken synchronization if it's possible that dsync is being run
concurrently for the same user.

-m mailbox

Synchronize only this mailbox name.

-n namespace

Synchronize only the specified namespace. This parameter can be used multiple times.

Use stateful synchronization. If the previous state is unknown, use an empty string. The new
state is always printed to standard output.

-u user/mask

Run the command only for the given user. It's also possible to use
'*' and '?' wildcards (e.g. -u *@example.org).
When neither the -A option, nor the -F file option, nor the
-u user was specified, the command will be executed with the environment
of the currently logged in user.

-x mailbox_mask

Exclude the specified mailbox name/mask. The mask may contain "?" and
"*" wildcards. This parameter can be used multiple times.

This is the same as remote, except "user@domain\n" is sent before dsync protocol
starts. This allows implementing a trusted wrapper script that runs doveadm dsync-server by reading
the username from the first line.

Synchronization was done without errors, but some changes couldn't be done, so the
mailboxes aren't perfectly synchronized. Running dsync again usually fixes this. Typically this
occurs for message modification sequences with newly created mailboxes. It can also occur if one of
the mailboxes change during the syncing.

Assuming that the mail_location setting in /etc/dovecot/conf.d/10-mail.conf is set
to: mail_location = mdbox:~/mdbox, a logged in system user may convert her/his mails from
its Maildir in her/his home directory to the mdbox mailbox format. The user has to execute the
command:

doveadm sync maildir:~/Maildir

If you want to do this without any downtime, you can do the conversion one user at a time.
Initially:

*

Configuration uses mail_location = maildir:~/Maildir

*

Set up the possibility of doing per-user mail location using userdb extra fields.

Then for each user:

1.

Run doveadm sync once to do the initial conversion.

2.

Run doveadm sync again, because the initial conversion could have taken a while and new
changes could have occurred during it. This second time only applies changes, so it should be
fast.

3.

Update mail extra field in userdb to mdbox:~/mdbox. If you're using auth cache, you
need to flush it, e.g. doveadm auth cache flush.

4.

Wait for a few seconds and then kill (doveadm kick) the user's all existing imap and pop3
sessions (that are still using maildir).

5.

Run doveadm sync once more to apply final changes that were possibly done. After this
there should be no changes to Maildir, because the user's mail location has been changed and
all existing processes using it have been killed.

Once all users have been converted, you can set the default mail_location to mdbox and
remove the per-user mail locations from userdb.